Systems and methods for dynamic control of heart failure therapy

ABSTRACT

Systems and methods for monitoring and treating patients with heart failure (HF) are discussed. The system may sense cardiac signals, and receives information about patient physiological or functional conditions. A stimulation parameter table that includes recommended values of atrioventricular delay (AVD) or other timing parameters maybe created at a multitude of patient physiological or functional conditions. The system may periodically reassess patient physiological or functional conditions. A therapy programmer circuit may dynamically switch between left ventricular-only pacing and biventricular pacing, or switch between single site pacing and multisite pacing based on the patient condition. The therapy programmer circuit may adjust AVD and other timing parameters using the cardiac signal input and the stored stimulation parameter table. A HF therapy may be delivered according to the determined stimulation site, stimulation mode, and the stimulation timing.

CLAIM OF PRIORITY

This application claims the benefit of priority under 35 U.S.C. § 119(e)of U.S. Provisional Patent Application Ser. No. 62/521,215, filed onJun. 16, 2017, which is herein incorporated by reference in itsentirety.

TECHNICAL FIELD

This document relates generally to medical systems and devices, and moreparticularly, to systems, devices, and methods of electrostimulation fortreating heart failure.

BACKGROUND

Congestive heart failure (CHF) is a leading cause of death in the UnitedStates and globally. CHF occurs when the heart is unable to adequatelysupply enough blood to maintain a healthy physiological state. CHF maybe treated by drug therapy, or by electrostimulation therapy.

Implantable medical devices (IMDs) have been used to monitor CHFpatients and manage heart failure in an ambulatory setting. Some IMDsmay include sensors to sense physiological signals from a patient, anddetect worsening heart failure, such as heart failure decompensation.Frequent patient monitoring and early detection of worsening heartfailure may help improve patient outcome. Identification of patient atan elevated risk of future heart failure events may help provide timelytreatment and prevent or reduce hospitalization. Identifying and safelymanaging the patients at risk of worsening heart failure can avoidunnecessary medical interventions, hospitalization, and reducehealthcare cost.

An IMD may include a pulse generator and electrical circuitry configuredto electrically stimulate a heart or other excitable tissue, to helprestore or improve the cardiac performance, or to correct cardiacarrhythmias. One example of the electrostimulation therapy is cardiacresynchronization therapy (CRT). CRT, typically delivered asbiventricular (BiV) pacing or synchronized left ventricle (LV)-onlypacing, may be indicated for CHF patients with moderate to severesymptoms and ventricular dyssynchrony. CRT keeps the LV and rightventricle (RV) pumping synchronously by sending electrical stimuli toboth the LV and RV. The synchronized stimulation may improve heartpumping efficiency and increase blood flow in some CHF patients. CRT candecrease hospitalization and morbidity associated with worsening heartfailure, as well as improvements in quality of life.

SUMMARY

Ambulatory medical devices (AMDs), such as IMDs, subcutaneous medicaldevices, wearable medical devices, or other external medical devices,may be used to detect worsening heart failure and deliver heart failure(HF) therapy to restore or improve the cardiac function. An IMD may becoupled to implanted leads with electrodes that may be used to sensecardiac activity, or to deliver HF therapy, such as cardiacelectrostimulation. An AMD may have functionality of programmabletherapy that allows for manual or automatic adjustment ofelectrostimulation parameters, such as stimulation chamber or site,stimulation mode, or stimulation timing.

An AMD may be configured to stimulation various cardiac chambers torestore cardiac synchrony and improve hemodynamics. During CRT or BiVpacing, synchronized stimulation may be applied to the LV and the RV ofa heart. The RV and LV pacing sites may be stimulated simultaneously, orsequentially with an RV-LV interventricular pacing delay (VVD). Deliveryof LV and RV pacing may be timed relative to a fiducial point, such asan intrinsic atrial depolarization sensed by an atrial electrode (atrialsense, or AS), or an atrial pacing pulse (AP) that elicits atrialactivation. If no intrinsic ventricular depolarization is detectedwithin a period of atrial-ventricular delay (AVD) following the AS orthe AP, the LV and RV pacing may be delivered at the end of the AVD.

As an alternative to BiV pacing, stimulation may be delivered only atone heart chamber, such as the LV. Such an LV-only pacing may offersatisfactory synchrony and cardiac performance in certain patients, suchas those with intact atrioventricular (AV) conduction requiring cardiacresynchronization. Compared to the BiV pacing, LV-only pacing mayrequire a simpler implantable procedure, consumes less power, andprovides increased battery longevity. As such, it is clinically a validalternative to more complicated BiV therapy regime. Similar to timing ofBiV pacing, the LV pacing may be delivered at the end of a programmedAVD subsequent to the AS or the AP if no intrinsic LV depolarization isdetected within the period of AVD.

An AMD may be configured to stimulate one or more sites of a heartchamber simultaneously or sequentially. In conventional single sitepacing (SSP), only one site of a particular heart chamber (e.g., the LV)is stimulated. Alternatively, multisite pacing (MSP) can be used to asan alternative to SSP. The MSP involves electrostimulation at two ormore sites in a heart chamber within a cardiac cycle. For example, in LVMSP, multiple LV sites may be simultaneously stimulated, or separated byone or more intra-LV time offset (ILVD).MSP may improve LV function andhemodynamic responses in some patients. However, MSP may require moreenergy than SSP, and may also increase the complexity of system designand operation. Not all CHF patients can uniformly benefit more from MSPthan SSP.

The stimulation timing parameters (e.g., AVD, VVD, or ILVD) define thetiming and sequence of cardiac stimulation, and may have an impact ontherapy efficacy and hemodynamic outcome. The stimulation timingparameters, such as AVD, may be determined using measurements of patientAV conduction, such as an interval (PRI) measured from surfaceelectrocardiogram (ECG) between a P wave and an R wave within a cardiaccycle, or an interval (AVI) measured from an intracardiac electrogram(EGM) between an atrial sensed (AS) or atrial paced (AP) event to aventricular sensed event (VS) within a cardiac cycle. In a patient, thePRI or AVI may not stay constant, but instead may vary under a multitudeof physiological or functional conditions. For example, long-termchanges in patient health conditions, HF progressions such as remodelingor decompensation, or short-term changes in heart rate, postures,posture transitions, physical activities, sleep/awake status,medication, hydration, diet, among other factors, may affect the PRI orAVI. Accordingly, the stimulation timing parameters such as AVD may alsobe affected by the long-term or short-term changes in patientconditions. Consequently, a HF therapy (e.g., LV-only pacing, BiVpacing, SSP, or MSP) based on a previously optimized AVD may no longerbe effective or provide satisfactory patient outcome at a differentpatient condition. For example, a programmed AVD may be too long whenpatient changes posture, resulting in reduced or less optimal CRTdelivery that adversely affects patient outcome.

The present inventors have recognized a number of technical challengesin electrostimulation therapy for HF. Among others, one challenge has todo with individualized HF therapy, particularly adverse impacts ofchanging patient conditions on therapy efficacy. In addition tointer-patient differences of responses to LV-only pacing versus BiVpacing, and responses to MSP versus SSP, there is intra-patientvariations over time of responses to LV-only pacing or BiV pacing, orresponses to SSP or MSP, at least because of an impact of the long-termand short-time changes in patient physiological or functionalconditions. Another challenge pertains to a guarantee of adequate pacingtherapy, particularly in pacing-dependent patients. For example,reduction of CRT pacing may occur in various occasions in a conventionalHF management system, such as during therapy optimization. Someconventional systems may reconfigure a pacing electrode (e.g., an LVpacing electrode) to sense cardiac electrical activity. Pacing therapymay have to be suspended, albeit temporarily, so as to provide eventsensing during therapy optimization process. For example, frequentreassessment of PRI or AVI when there is a changing patient conditionmay require reconfiguring the pacing electrode as a sensing electrode tosense ventricular activation. Suspension of pacing for frequentreassessment of PRI or AVI, even temporarily, may adversely affectpatient outcome. Frequent electrode reconfiguration may also add cost incomputational resources such as firmware cycle, and reduce battery life.

This document discusses, among other things, a patient management systemfor monitoring and treating patients with heart failure. The system mayinclude a sensor circuit to sense cardiac signals, and a receiver toreceive information about patient physiological or functional conditionssuch as posture and physical activities. Stimulation timing parametersunder specified patient physiological or functional conditions may bedetermined and stored in a memory. The system may periodically reassesspatient physiological or functional conditions. A therapy programmercircuit may dynamically determine, for a specific patient condition, oneor more of a stimulation site, a stimulation mode, or stimulation timingusing the sensor input and the stored stimulation timing parametersvalues. The system may include a therapy circuit to deliver or adjust anelectrostimulation therapy according to the determined stimulation site,stimulation mode, and the stimulation timing.

The present document provides technical solutions to theabove-identified challenges in electrostimulation therapy for HF, andtherefore improves the medical technology of device-based heart failurepatient management. Among other things, the present document providesapproaches for providing cardiac pacing therapy (e.g., throughprogramming therapy parameters including stimulation timing, stimulationsite, and stimulation mode) tailored to individual patient and toparticular patient physiological or functional condition. This documentdiscusses an efficient approach of adjusting AVD or other stimulationtiming parameters based on a stimulation parameter table that containsrecommended AVD values at a multitude of patient conditions. The patientcondition-indicated adjustment of stimulation timing, along with thedynamic switching between LV-only pacing and BiV and dynamic switchingbetween SSP and MSP pacing mode, may ensure consistent and effectivepacing therapy to meet individual patient need under differentphysiological or functional conditions. In an example, this documentprovides a beat-to-beat adjustment of stimulation timing and switchingof stimulation site or stimulation mode. The systems and methodsdiscussed herein may improve therapy efficacy, patient outcome, andreduce healthcare cost associated with HF management. The presentdocument also provides identification of the conditions that may affectstimulation timing and therapy efficacy. This may be beneficial forhealthcare providers to track patient HF progression, and improvepatient management.

This document also discusses a method to estimate the PRI or AVI duringstimulation using an offset between an AVD corresponding to apseudofusion beat and a PRI or AVI. Because the estimation processrequires no suspension of pacing, sufficient pacing therapy can beachieved even during therapy adjustment; and the adverse effects onpatient outcome can be avoided or reduced.

In addition to the improvement in the medical technology of device-basedheart failure patient management under various patient conditions, thesystems, devices, and methods discussed herein may also allow for moreefficient device memory usage, such as by storing and updating thestimulation timing parameter that are clinically more relevant topatient long-term and short-term changing conditions. The individualizedand dynamically adjusted therapy discussed in this document may not onlyimprove therapy efficacy and patient outcome, but may also save devicepower and extend battery life. With individualized HF therapy tailoredto specific patient conditions, fewer unnecessary interventions orhospitalizations may be scheduled, prescribed, or provided; as a result,overall cost savings may be realized.

This Summary is an overview of some of the teachings of the presentapplication and not intended to be an exclusive or exhaustive treatmentof the present subject matter. Further details about the present subjectmatter are found in the detailed description and appended claims. Otheraspects of the invention will be apparent to persons skilled in the artupon reading and understanding the following detailed description andviewing the drawings that form a part thereof, each of which are not tobe taken in a limiting sense. The scope of the present invention isdefined by the appended claims and their legal equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are illustrated by way of example in the figures ofthe accompanying drawings. Such embodiments are demonstrative and notintended to be exhaustive or exclusive embodiments of the presentsubject matter.

FIG. 1 illustrates an example of a patient management system andportions of an environment in which the system may operate.

FIG. 2 illustrates an example of a dynamically controlled cardiacstimulation system configured to program and deliver electrostimulationto treat HF or other cardiac diseases.

FIGS. 3A-3B illustrate examples of a stimulation parameter tableincluding recommended values of stimulation timing at various patientphysiological and physical conditions.

FIGS. 4A-B illustrate examples of methods for initializing and updatinga stimulation parameter table.

FIG. 5 illustrates an example of a method for dynamic determination ofPRI or AVI during pacing.

FIG. 6 illustrates an example of a method for determining betweenLV-only pacing and BiV pacing.

FIG. 7 illustrates an example of a method for determining between SSPpacing and MSP.

FIG. 8 illustrates a block diagram of an example machine upon which anyone or more of the techniques (e.g., methodologies) discussed herein mayperform.

DETAILED DESCRIPTION

Disclosed herein are systems, devices, and methods for monitoring andtreating patients with heart failure or other cardiac diseases. Thesystem may sense cardiac signals, and receives information about patientphysiological or functional conditions. A stimulation parameter tablethat includes recommended values of timing parameters such as AVD may becreated at a multitude of patient physiological or functionalconditions. The system may periodically reassess patient physiologicalor functional conditions. A therapy programmer circuit may dynamicallyswitch between LV-only pacing and BiV pacing, switch between single sitepacing and multi-site pacing based on the patient condition, or adjustthe stimulation timing using the cardiac signal input and thestimulation parameter table. A HF therapy may be delivered in accordancewith the determined stimulation site, stimulation mode, and thestimulation timing.

System and Apparatus for HF Monitoring and Therapy

FIG. 1 illustrates an example of a patient management system 100 andportions of an environment in which the patient management system 100may operate. The patient management system 100 may include an ambulatorymedical device, such as an implantable medical device (IMD) 110 that maybe electrically coupled to a heart 105 through one or more leads 108A-C,and an external system 120 that may communicate with the IMD 110 via acommunication link 103. Examples of the IMD 110 may include, but are notlimited to, pacemakers, defibrillators, cardiac resynchronizationtherapy (CRT) devices, cardiac remodeling control therapy (RCT) devices,neuromodulators, drug delivery devices, biological therapy devices,diagnostic devices such as cardiac monitors or loop recorders, orpatient monitors, among others. The IMD 110 may be coupled to, or may besubstituted by a monitoring medical device such as a bedside or otherexternal monitor. In addition to or in lieu of the IMD 110, otherambulatory medical device may be used, which may include subcutaneousmedical device such as a subcutaneous monitor or diagnostic device, orexternal monitoring or therapeutic medical devices such as automaticexternal defibrillators (AEDs) or Holter monitors; wearable medicaldevices such as patch-based devices, smart watches, or smartaccessories; or a bedside monitor.

The IMD 110 may include a hermetically sealed can 112 that may house anelectronic circuit that may sense a physiological signal in the heart105 and may deliver one or more therapeutic electrical pulses to atarget region, such as in the heart, such as through one or more leads108A-C. The patient management system 100 may include only one lead suchas 108B, or may include two leads such as 108A-B.

The lead 108A may include a proximal end that may be connected to IMD110 and a distal end that may be placed at a target location such as inthe right atrium (RA) 131 of the heart 105. The lead 108A may have afirst pacing-sensing electrode 141 that may be located at or near itsdistal end, and a second pacing-sensing electrode 142 that may belocated at or near the electrode 141. The electrodes 141 and 142 may beelectrically connected to the IMD 110 such as via separate conductors inthe lead 108A, such as to allow for sensing of the right atrial activityand optional delivery of atrial pacing pulses. The lead 108B may be adefibrillation lead that may include a proximal end that may beconnected to IMD 110 and a distal end that may be placed at a targetlocation such as in the right ventricle (RV) 132 of heart 105. The lead108B may have a first pacing-sensing electrode 152 that may be locatedat distal end, a second pacing-sensing electrode 153 that may be locatednear the electrode 152, a first defibrillation coil electrode 154 thatmay be located near the electrode 153, and a second defibrillation coilelectrode 155 that may be located at a distance from the distal end suchas for superior vena cava (SVC) placement. The electrodes 152 through155 may be electrically connected to the IMD 110 such as via separateconductors in the lead 108B. The electrodes 152 and 153 may allow forsensing of a ventricular EGM and may optionally allow delivery of one ormore ventricular pacing pulses, and electrodes 154 and 155 may allow fordelivery of one or more ventricular cardioversion/defibrillation pulses.In an example, the lead 108B may include only three electrodes 152, 154and 155. The electrodes 152 and 154 may be used for sensing or deliveryof one or more ventricular pacing pulses, and the electrodes 154 and 155may be used for delivery of one or more ventricular cardioversion ordefibrillation pulses. The lead 108C may include a proximal end that maybe connected to the IMD 110 and a distal end that may be placed at atarget location such as in a left ventricle (LV) 134 of the heart 105.The lead 108C may be implanted through the coronary sinus 133 and may beplaced in a coronary vein over the LV such as to allow for delivery ofone or more pacing pulses to the LV. The lead 108C may include anelectrode 161 that may be located at a distal end of the lead 108C andanother electrode 162 that may be located near the electrode 161. Theelectrodes 161 and 162 may be electrically connected to the IMD 110 suchas via separate conductors in the lead 108C such as to allow for sensingthe LV EGM and optionally allow delivery of one or moreresynchronization pacing pulses from the LV. Additional electrodes maybe included in or along the lead 108C. In an example, as illustrated inFIG. 1, a third electrode 163 and a fourth electrode 164 may be includedin the lead 108. In some examples (not shown in FIG. 1), at least one ofthe leads 108A-C, or an additional lead other than the leads 108A-C, maybe implanted under the skin surface without being within at least oneheart chamber, or at or close to heart tissue.

The IMD 110 may include circuitry that may sense a physiological signal.The physiological signal may include an EGM or a signal representingmechanical function of the heart 105. The hermetically sealed can 112may function as an electrode such as for sensing or pulse delivery. Forexample, an electrode from one or more of the leads 108A-C may be usedtogether with the can housing 112 such as for unipolar sensing of an EGMor for delivering one or more pacing pulses. A defibrillation electrodefrom the lead 108B may be used together with the can housing 112 such asfor delivering one or more cardioversion/defibrillation pulses. In anexample, the IMD 110 may sense impedance such as between electrodeslocated on one or more of the leads 108A-C or the can housing 112. TheIMD 110 may be configured to inject current between a pair ofelectrodes, sense the resultant voltage between the same or differentpair of electrodes, and determine impedance using Ohm's Law. Theimpedance may be sensed in a bipolar configuration in which the samepair of electrodes may be used for injecting current and sensingvoltage, a tripolar configuration in which the pair of electrodes forcurrent injection and the pair of electrodes for voltage sensing mayshare a common electrode, or tetrapolar configuration in which theelectrodes used for current injection may be distinct from theelectrodes used for voltage sensing. In an example, the IMD 110 may beconfigured to inject current between an electrode on the RV lead 108Band the can housing 112, and to sense the resultant voltage between thesame electrodes or between a different electrode on the RV lead 108B andthe can housing 112. A physiological signal may be sensed from one ormore physiological sensors that may be integrated within the IMD 110.The IMD 110 may also be configured to sense a physiological signal fromone or more external physiological sensors or one or more externalelectrodes that may be coupled to the IMD 110. Examples of thephysiological signal may include one or more of ECG, intracardiac EGM,heart rate, heart rate variability, intrathoracic impedance,intracardiac impedance, arterial pressure, pulmonary artery pressure,left atrial pressure, RV pressure, LV coronary pressure, coronary bloodtemperature, blood oxygen saturation, one or more heart sounds, physicalactivity or exertion level, physiological response to activity, posture,respiration, body weight, or body temperature, among others.

In certain examples, the system 100 may include one or more leadlesssensors not being tethered to the IMD 110 via the leads 108A-C. Theleadless ambulatory sensors may be configured to sense a physiologicalsignal and wirelessly communicate with the IMD 110. In some examples,the IMD 110 may be a leadless medical device. Unlike a tethered devicesuch as the IMD 110 as illustrated in FIG. 1, a leadless medical devicerequires no lead, wire, or tether extended between the electrodes andthe device body. The leadless medical device may include an anchoring orfixation mechanism for positioning the device body on a target implantside, such as an endocardial surface of one of a left ventricle, a rightventricle, a left atrium, or a right atrium, or an epicardial surface ofa portion of the heart. The leadless medical device may be deliveredtransvenously and positioned within a blood vessel on the heart, such asa coronary vein, where one or more electrodes on the leadless medicaldevice may be directly or indirectly in contact with the epicardialsurface of the heart. An example of such an leadless medical device mayinclude the leadless cardiac pacemaker (LCP) disclosed in the commonlyassigned U.S. Patent Application Publication US2016/0051823 by Maile etal., entitled “LEADLESS CARDIAC PACEMAKER HAVING A SENSOR WITH A LOWERPOWER MODE,” which is hereby incorporated by reference in its entirety.

The arrangement and functions of these leads and electrodes aredescribed above by way of example and not by way of limitation.Depending on the need of the patient and the capability of theimplantable device, other arrangements and uses of these leads andelectrodes are possible.

The patient management system 100 may include a dynamically controlledstimulation circuit 113. The dynamically controlled stimulation circuit113 may determine therapy parameters dynamically according to patientpresent physiological or functional condition. Patient conditions suchas patient health status, HF progressions, remodeling or decompensation,heart rate, postures, posture transitions, physical activities,sleep/awake status, medication, hydration, diet, among other factors,may affect cardiac electrical and mechanical properties, andconsequently affect HF therapy efficacy. In an example, the dynamicallycontrolled stimulation circuit 113 may determine a stimulation site suchas between a LV-only pacing and a BiV pacing, or a stimulation mode suchas between a SSP and MSP, based on the sensor input. The dynamicallycontrolled stimulation circuit 113 may further determine stimulationtimings such as AVD or VVD values using the sensor input and optionallya pre-determined stimulation parameter table. The stimulation parametertable contains timing values (e.g., AVD values) under various patientphysical and physiological conditions. The dynamically controlledstimulation circuit 113 may deliver electrostimulation to the heart inaccordance with the determined stimulation site, stimulation mode, andthe stimulation timing parameters. Examples of the dynamicallycontrolled stimulation circuit 113 are described below, such as withreference to FIG. 2.

The external system 120 may allow for programming of the IMD 110, andreceiving information from the IMD 110, via a communication link 103.The external system 120 may include a local external IMD programmer. Theexternal system 120 may include a remote patient management system thatmay monitor patient status or adjust one or more therapies such as froma remote location. The remote patient management system may evaluatecollected patient data and provide alert notifications, among otherpossible functions. In an example, the remote patient management systemmay include a centralized server acting as a central hub for collectedpatient data storage and analysis. The server may be configured as auni-, multi- or distributed computing and processing system. The remotepatient management system may additionally or alternatively include oneor more locally configured clients or remote clients securely connectedto the server. Examples of the clients may include personal desktops,notebook computers, mobile devices, or other computing devices. Systemusers, such as clinicians or other qualified medical specialists, mayuse the clients to securely access stored patient data assembled in thedatabase in the server.

The communication link 103 may include one or more of an inductivetelemetry link, a radio-frequency telemetry link, or a telecommunicationlink, such as an internet connection. The communication link 103 mayprovide for data transmission between the IMD 110 and the externalsystem 120. The transmitted data may include, for example, real-timephysiological data acquired by the IMD 110, physiological data acquiredby and stored in the IMD 110, therapy history data or data indicatingIMD operational status, programming instructions to the IMD 110 such asto configure the IMD 110 to perform one or more actions including, forexample, data acquisition, device self-diagnostic test, or therapydelivery.

The dynamically controlled stimulation circuit 113 may be implemented atthe external system 120 such as using data extracted from the IMD 110 ordata stored in a memory within the external system 120. Portions of thedynamically controlled stimulation circuit 113 may be distributedbetween the IMD 110 and the external system 120.

Portions of the IMD 110 or the external system 120 may be implementedusing hardware, software, or any combination of hardware and software.Portions of the IMD 110 or the external system 120 may be implementedusing an application-specific circuit that may be constructed orconfigured to perform one or more particular functions, or may beimplemented using a general-purpose circuit that may be programmed orotherwise configured to perform one or more particular functions. Such ageneral-purpose circuit may include a microprocessor or a portionthereof, a microcontroller or a portion thereof, or a programmable logiccircuit, or a portion thereof. For example, a “comparator” may include,among other things, an electronic circuit comparator that may beconstructed to perform the specific function of a comparison between twosignals or the comparator may be implemented as a portion of ageneral-purpose circuit that may be driven by a code instructing aportion of the general-purpose circuit to perform a comparison betweenthe two signals. While described with reference to the IMD 110, thepatient management system 100 could include a subcutaneous medicaldevice (e.g., subcutaneous ICD, subcutaneous diagnostic device),wearable medical devices (e.g., patch based sensing device), or otherexternal medical devices.

FIG. 2 illustrates an example of a dynamically controlled cardiacstimulation system 200. The dynamically controlled cardiac stimulationsystem 200 may be configured to provide diagnostic informationincluding, for example, changes of cardiac status at various patientphysiological or functional conditions, and recommend therapy parametersvalues such as timing, site, and mode of cardiac electrostimulation. Thedynamically controlled cardiac stimulation system 200 may include one ormore of a cardiac sensor circuit 210, a patient condition receiver 220,a therapy programmer circuit 230, a memory circuit 240, a controllercircuit 250, and a user interface 260. In some examples, the dynamicallycontrolled cardiac stimulation system 200 may additionally include atherapy circuit 270 that may deliver or adjust a therapy such as cardiacelectrostimulation. At least a portion of the cardiac monitoring system200 may be implemented in an AMD, such as the IMD 110, or distributedbetween an AMD or and an external system such as the external system120.

The cardiac sensor circuit 210 may include a sense amplifier to sense acardiac signal. The cardiac signal may be sensed from different heartchambers, such as one or more of the RA, the RV, the left atrium (LA),or the LV. The cardiac signal may be sensed when the heart undergoes anintrinsic rhythm such as a sinus rhythm, or when the heart is stimulatedin accordance with a stimulation protocol, such as pacing at an atrium,a ventricle, or other sites at a specified rate or timing sequence.Examples of the cardiac signal may include cardiac electrical signalssuch as ECGs sensed non-invasively from body surface, subcutaneous ECGssensed from subcutaneously placed electrodes, or intracardiac EGMssensed from electrodes on one or more of the leads 108A-C or the canhousing 112. By way of example and not limitation, atrial activation(denoted by AS) may be sensed using a sensing vector comprising one ofthe atrial electrodes 141 or 142, right ventricular activation (denotedby RVS) may be sensed using a sensing vector comprising one of the RVelectrodes 152-154, and left ventricular activation (denoted by LVS) maybe sensed using a sensing vector comprising one of the LV electrodes161-164.

Additionally or alternatively, the cardiac signals may include signalsindicative of cardiac mechanical activities or patient hemodynamicstatus. In an example, the cardiac signal may include a signal sensedfrom an accelerometer or a microphone configured to sense heart soundsin a patient. In an example, the cardiac signal may include a cardiac orthoracic impedance signal. The cardiac mechanical signals may includeblood pressure sensor signals or any other sensor signals indicative ofcardiac mechanical activities or hemodynamic status.

In some examples, the cardiac sensor circuit 210 may simultaneously orsequentially sense two or more cardiac signals from different sites of aheart chamber, such as multiple sites at the LV. The cardiac sensorcircuit 210 may sense LV EGMs from two or more LV sites using respectivesensing vectors. An example of the LV sensing vector may include abipolar sensing vector, such as between a pair of electrodes selectedamong 161-164. Alternatively, the LV sensing vector may be between oneof the electrodes 161-164 and another electrode positioned on adifferent chamber or on a different lead (such as one of electrodes152-155 on the RV lead 108B, or electrodes 141 or 142 on the RA lead108A). Another example of the LV sensing vector may include a unipolarsensing vector such as between one of the electrodes 161-164 and the canhousing 112.

The cardiac sensor circuit 210 may process the sensed cardiac signal,including amplification, digitization, filtering, or other signalconditioning operations. From the processed cardiac signal, the cardiacsensor circuit 210 may detect signal features, or perform measurementsthat indicate patient cardiac condition or therapy efficacy, or acomplication introduced by the stimulation. Examples of the signalfeatures may include temporal or morphological features indicative ofintrinsic cardiac activity such as a P wave, Q wave, R wave, QRScomplex, or T wave that may be detected from a surface ECG, asubcutaneous ECG, or an intracardiac EGM, timing and intensity of evokedcardiac activity such as evoked electrical or mechanical activation inresponse to an electrostimulation of the heart. Examples of theintensity measurement may include signal amplitude, slope or rate ofchange of signal amplitude, amplitude of a transformed physiologicalsignal such as integrated signal, or a frequency-domain measurement suchas power spectral density. Examples of the timing measurement mayinclude a time delay between cardiac activations sensed at differentheart chambers (e.g., PRI or AVI between an atrium and a ventricle, orRV to LV sensed interval), or between different pacing sites (e.g.,sensing delay among various LV sites).

The patient condition receiver 220 may receive information about patientlong-term and short-term physiological or functional conditions. Changesin long-term or short-term patient conditions may affect cardiacelectrical and mechanical properties and patient hemodynamic responses.As a result, a therapy may be less effective if not timely and properlyadjusted to accommodate the changing patient condition. Physiologicalsignals, such as cardiac, pulmonary, neural, or biochemical signals, maybe received at the patient condition receiver 220. Examples of thephysiological signals may include ECG, intracardiac EGM, a heart ratesignal, a heart rate variability signal, a cardiovascular pressuresignal, a heart sounds signal, a respiratory signal, a thoracicimpedance signal, a respiratory sounds signal, or blood chemistrymeasurements or expression levels of one or more biomarkers. Examples ofthe functional signals may include patient posture, gait, balance, orphysical activity signals, among others. The sensor circuit may sensethe functional signals using a motion sensor, such as an accelerometer,gyroscope (which may be a one-, two-, or three-axis gyroscope),magnetometer (e.g., a compass), inclinometers, goniometers, altimeters,electromagnetic tracking system (ETS), or a global positioning system(GPS) sensor, among others. In another example, the functional signalmay include information about sleep state signal, such as sleep or awakestate, frequency or duration of sleep position switch, sleep incline, orother indicators of sleep quality. In another example, the functionalsignal may include information on food or drink intake (e.g., swallow),coughing or aspiration detection. In some examples, information aboutpatient physiological or functional conditions may be stored in astorage device, such as an electronic medical record (EMR) system, andthe patient condition receiver 220 may be configured to receive thepatient condition from the storage device in response to a user input ortriggered by a specific event.

In some examples, the patient condition receiver 220 may receiveinformation about patient medical history, medication intake,hospitalization, surgical procedures, cardiac remodeling, worseningheart failure events such as heart failure decompensation, or HFcomorbidities. In some examples, the patient condition receiver 220 mayreceive device implant information, such as position of an implantablelead. For example, an LV lead 108C may be implanted at free wall,anterior, lateral, or posterior, among other possible LV positions. LVlead location may affect the therapy efficacy, and be used fordetermining the stimulation site, mode, and timing parameter. In someexamples, the patient condition receiver 220 may additionally includepatient echocardiography-derived measurements, such as ejectionfraction, cardiac contractility, cardiac timing, or aortic velocity,among other hemodynamic parameters or other clinical diagnostics.

The therapy programmer circuit 230 may generate diagnostics aboutchanges of cardiac status at a particular patient physiological orfunctional condition as received from the patient condition receiver220, and recommend therapy parameter values including, for example,timing, site, and mode of cardiac electrostimulation. The therapyprogrammer circuit 230 may be implemented as a part of a microprocessorcircuit, which may be a dedicated processor such as a digital signalprocessor, application specific integrated circuit (ASIC),microprocessor, or other type of processor for processing informationincluding physical activity information. Alternatively, themicroprocessor circuit may be a general-purpose processor that mayreceive and execute a set of instructions of performing the functions,methods, or techniques described herein.

The therapy programmer circuit 230 may include circuit sets comprisingone or more other circuits or sub-circuits, including one or more of aPRI/AVI estimator circuit 235, a stimulation site selector circuit 231,a stimulation mode selector 232, and a stimulation timing adjustercircuit 233. These circuits may, alone or in combination, perform thefunctions, methods, or techniques described herein. In an example,hardware of the circuit set may be immutably designed to carry out aspecific operation (e.g., hardwired). In an example, the hardware of thecircuit set may include variably connected physical components (e.g.,execution units, transistors, simple circuits, etc.) including acomputer readable medium physically modified (e.g., magnetically,electrically, moveable placement of invariant massed particles, etc.) toencode instructions of the specific operation. In connecting thephysical components, the underlying electrical properties of a hardwareconstituent are changed, for example, from an insulator to a conductoror vice versa. The instructions enable embedded hardware (e.g., theexecution units or a loading mechanism) to create members of the circuitset in hardware via the variable connections to carry out portions ofthe specific operation when in operation. Accordingly, the computerreadable medium is communicatively coupled to the other components ofthe circuit set member when the device is operating. In an example, anyof the physical components may be used in more than one member of morethan one circuit set. For example, under operation, execution units maybe used in a first circuit of a first circuit set at one point in timeand reused by a second circuit in the first circuit set, or by a thirdcircuit in a second circuit set at a different time.

The stimulation site selector circuit 231 may be configured to determinea heart chamber for pacing according to the received patient condition.In an example, the stimulation site selector circuit 231 may selectbetween an LV-only pacing and a BiV pacing. The BiV pacing refers tostimulation of both the LV and RV simultaneously or sequentially with aspecified time offset. In some patients, the BiV pacing may offer bettercardiac synchrony and cardiac contractility than the LV-only pacingconfigured for only stimulating the LV. However, a change in patientphysiological or functional condition (e.g., a heart rate increase, or aposture transition from supine to standing) may alter AV condition,ventricular contractility, or other cardiac properties. Pacing chambermay need to be switched, among other therapy adjustments, to maintainadequate therapy efficacy. The stimulation site selector circuit 231 mayinitiate stimulation site assessment in response to a change of patientcondition, and determine between an LV-only pacing and BiV pacing basedon a heart rate increase, and an indicator of AV conduction abnormality,such as an extension of PRI or AVI or increased irregularity of the PRIor AVI. Examples of determining stimulation site between LV-only pacingand BiV pacing to accommodate changes in patient conditions arediscussed below, such as with reference to FIG. 6.

The stimulation mode selector circuit 232 may be configured to determinebetween a single site pacing (SSP) and a multisite pacing (MSP)according to the received patient condition. The MSP may be delivered attwo or more sites inside, or on an epicardial surface of, one or moreheart chambers or tissues surrounding any of the chambers. During MSP,pulse trains may be delivered at the two or more cardiac sitessimultaneously, or sequentially with an intra-ventricular delay lessthan a sensed or paced time interval value of the cardiac cycle.

In an example, the stimulation mode selector circuit 232 may initiatestimulation mode assessment in response to a change of patientcondition, and determine between SSP pacing and a MSP pacing at two ormore LV sites using inter-ventricular intervals measured from RV site tovarious candidate LV sites, such as those corresponding to the LVelectrodes 161-164. The inter-ventricular intervals represent degrees ofdyssynchrony between RV and various LV sites. The stimulation modeselector circuit 232 may scan through a plurality of candidate LVelectrodes to identify those LV sites with the correspondinginter-ventricular intervals satisfying a specified condition, such as apatient condition-indicated threshold value, and select SSP or MSP basedon the candidate electrodes identification. Examples of determiningstimulation mode between SSP and MSP to accommodate changes in patientconditions are discussed below, such as with reference to FIG. 7.

The stimulation timing adjuster circuit 233 may be configured todetermine a stimulation timing parameter (e.g., AVD, VVD, or ILVD)according to the received patient condition. The stimulation timingparameters define the timing sequence of cardiac activation, and mayaffect therapy efficacy and patient hemodynamic response. In an example,the stimulation timing adjuster circuit 233 may determine AVD using PRIor AVI under the received patient condition. As previously discussed,the PRI or AVI may vary under a multitude patient physiological orfunctional conditions. PRI or AVI may be measured directly from thesensed cardiac signal under a specific patient condition. Alternatively,the PRI or AVI may be estimated dynamically during pacing, such asprovided by the PRI/AVI estimator circuit 235.

The AVD may be determined as a linear combination of an interval betweenatrial sensed (AS) or atrial paced (AP) activation to a sensed RVactivation (RVS), and an interval between AS or AP to a sensed LVactivation (LVS). Alternatively, AVD values under various patientconditions may be dynamically created and stored in the memory circuit240. Graphically, the AVD values may be organized in a stimulationparameter table, such as that depicted in FIGS. 3A-3B below. Thestimulation timing adjuster circuit 233, coupled to the memory circuit240, may search for the received patient condition from the stimulationparameter table, and identify a recommended AVD corresponding to thatpatient condition. The stimulation timing adjuster circuit 233 mayperform dynamic AVD adjustment by switching to the applicable tableentry whenever the patient is in that condition. In an example, the AVDmay be adjusted on a beat-by-beat basis. Examples of adjusting AVD usinga patient condition-indicated stimulation parameter table are discussedbelow, such as with reference to FIGS. 3-4.

The PRI/AVI estimator circuit 235 may be configured to dynamicallydetermine PRI or AVI during pacing. The PRI/AVI estimator circuit 235may be coupled to one or more of the stimulation site selector circuit231, the stimulation mode selector circuit 232, or the stimulationtiming adjuster circuit 233. The circuits 231-233 may use thedynamically determined PRI or AVI to update the stimulation parametertable, or to determine between LV-only pacing and BiV pacing, or todetermine between SSP and MSP.

The PRI/AVI estimator circuit 235 may be configured to measure an offsetbetween an AVD corresponding to a pseudofusion beat and a PRI or AVI,such as through a testing process, as to be discussed in the followingwith reference to FIG. 5. The offset may be stored for future use. Whena change patient physiological or functional condition is detected, thePRI or AVI may be estimated using a combination of the AVD that leads topseudofusion and the stored offset. As such, the PRI or AVI may beestimated without suspension of ventricular pacing. Examples of dynamicdetermination of PRI or AVI during pacing are discussed below, such aswith reference to FIG. 5.

The therapy circuit 270 may be configured to generate therapy accordingto the parameter values generated and recommended by the therapyprogrammer circuit 230. The therapy may include electrostimulationdelivered to the pacing sites via one or more of the leads 108A-C andthe respectively attached electrodes. The therapy circuit 270 may beconfigured to deliver LV-only pacing, or BiV pacing. Additionally oralternatively, the therapy circuit 270 may be configured to generate SSPfor stimulating one cardiac site, or a MSP for stimulating two or moresites of the heart within the same cardiac cycle. In an example, the MSPmay be delivered within the LV. The LV MSP may have a unipolar pacingconfiguration where only one electrode (e.g., the cathode) is a LVelectrode and the other electrode (e.g., the anode) is the IMD canhousing 112. In another example, a true bipolar configuration may beused, where both the cathode and anode are LV electrodes. In yet anotherexample, an extended bipolar configuration may be used, where oneelectrode (e.g., the cathode) is a LV electrode and the other electrode(e.g., the anode) is a RA electrode such as one of the electrodes 141 or142, or a RV electrode such as one of the electrodes 152-155. In anotherexample, a tripolar configuration may be used, which may involve two LVelectrodes used jointly as the cathode, or two electrodes such asselected from the RA and RV electrodes used jointly as the anode. Insome examples, one or more LV electrodes may be distributed in one ormore LV leads, catheters, or untethered pacing units.

In some examples, the therapy circuit 270 may initiate or adjustelectrostimulation at non-cardiac tissues such as nerve tissues, orother therapy types, such as a cardioversion therapy, a defibrillationtherapy, or drug therapy including delivering drug to a tissue or organ.In some examples, the therapy circuit 270 may modify an existingtherapy, such as adjust a stimulation parameter or drug dosage.

The controller circuit 250 may control the operations of the therapyprogrammer circuit 230, the memory circuit 240, the therapy circuit 270,and the data flow and instructions between these components andrespective subcomponents. In an example, the controller circuit 250 mayupdate the stimulation parameter table. The stimulation parameter tablemay be updated periodically, or in response to a trigger event. In someexamples, the controller circuit 250 may update the stimulationparameter table at a frequency according to table update history, suchas a trend of table update, such that next update may be scheduledaccording to the historical trend. Examples of creating and updating thestimulation parameter table are discussed below, such as with referenceto FIG. 4. The controller circuit 250 may additionally control thetherapy circuit 270 to deliver HF therapy according to the selectedstimulation site, stimulation mode, and the stimulation timingparameters.

The user interface 260 may include an input device that enables a systemuser to program the parameters used for electrostimulation or forsensing the cardiac signals. Examples of the input device may include akeyboard, on-screen keyboard, mouse, trackball, touchpad, touch-screen,or other pointing or navigating devices. The input device may enable thesystem user to activate automated programming of HF therapy, such asautomated determination of stimulation site, stimulation mode, andstimulation timing parameters under a specific patient condition. Theinput device may also enable the system user to confirm, reject, orotherwise modify the automatically determined therapy programming.

The user interface 260 may include a display for display therapyprogramming such as automatically determined stimulation site,stimulation mode, and stimulation timing parameters. The output unit 230may include a printing device for producing a hardcopy of theinformation. The information may be presented in a table, a chart, atrend, a diagram, or any other types of textual, tabular, or graphicalpresentation formats. Additional information for displaying may includecardiac signals sensed from the cardiac sensor circuit 210, signalfeatures or measurements (e.g., PRI or AVI) derived from the sensedcardiac signal, information of patient physiological or functionalconditions received from the patient condition receiver 220, or devicestatus information such as lead impedance and integrity, battery statussuch as remaining lifetime of the battery, or cardiac stimulationthreshold, or complications associated with stimulation at one or morecardiac sites, among others.

Patient Condition-Indicated Pacing Optimization

FIGS. 3A-3B illustrate examples of a stimulation parameter table thatincludes recommended values of stimulation timing at various patientphysiological and physical conditions. Examples of the conditions mayinclude posture (e.g., supine, sitting, standing, among other postures,or transitions between postures), walking, running, sleeping, time ofday (e.g., daytime, nighttime, or a particular duration during the day),diet, hydration, medication intake, heart rate, heart rate variability,arrhythmic events (e.g., atrial fibrillation, ventricular tachycardia,premature ventricular contractions, post arrhythmia), atrial activationmode (e.g., atrial pace or atrial sense), among others. The presentinventors have recognized that said conditions, individually or incombination, may affect cardiac tissue properties and patienthemodynamics. As a result, a therapy programmed under one condition maynot be equally effective under a different condition. Different AVDvalues may be recommended at different patient conditions to achievedesirable therapy efficacy and patient outcome.

Table 300 shown in FIG. 3A and table 350 shown in FIG. 3B may each beimplemented as a multi-dimensional array, an association map, or otherdata structures for storing in the memory circuit 240. By way of exampleand not limitation, the table 300 includes stimulation timing values,such as AVD values, at specific heart rate (HR) 310, posture 320, andatrial activation mode 330. The HR 310 may be categorized into aplurality of HR ranges, the posture 320 may include one or more of asupine, a sitting, or a standing posture, and the atrial activation mode330 may include one or more of atrial sense (AS) and atrial pace (AP)modes. The AVD for AS is hereinafter referred to sensed AVD, and the AVDfor AP is hereinafter referred to paced AVD. Each entry of the table 300may include a recommended AVD value under a corresponding patientcondition. For example, table entry 301 contains a recommended pacedAVD, denoted by AVD*, corresponding to a heart rate falling within 60-70bpm range and a standing posture. When the AVD* is programmed to thetherapy circuit, a ventricular pacing pulse may be delivered followingan atrial pace at an offset of AVD* if no intrinsic ventricular activityis detected within the period of AVD*. In some examples, the table 300may include stimulation timing values (e.g., AVD values) at specificheart rate (HR) 310 and atrial activation mode 330 regardless of patientposture. In other words, the posture 320 may be excluded from the table300. Table 350 shown in FIG. 3B includes stimulation timing values, suchas AVD values, at specific HR 310, time of a day 340, and the atrialactivation mode 330. By way of non-limiting example and as illustratedin FIG. 3B, the time of a day 340 may include daytime and nighttime.Each entry of the table 350 may include a recommended AVD value under acorresponding patient condition. For example, table entry 302 contains arecommended paced AVD, denoted by AVD*, corresponding to a heart ratefalling within 60-70 bpm range during a nighttime. In an example, thetime of a day 340 may include a number of time periods during a daywithin a 24-hour period. In various examples, the table 300 or 350 maybe augmented to include other conditions. For example, the table 300 mayinclude time of a day 340, or the table 350 may include informationabout patient posture 320. Various combination or permutations ofpatient conditions, including but not limited to the HR 310, posture320, atrial activation mode 330, and time of a day 340, have beencontemplated by the present inventors to be implemented in a stimulationparameter table similar to the table 300 or 350, which is within thescope of the present document.

In various examples, at least some entries of the table 300 or 350 mayadditionally or alternatively include recommended values of stimulationtiming parameters other than AVD. In an example, the table entry mayinclude a recommended RV-LV delay (VVD) under corresponding patientconditions of heart rate, posture, and atrial activation mode. The VVDrepresents an offset between an LV pacing pulse and a RV pacing pulsewithin a cardiac cycle for BiV pacing or CRT therapy such as selected bya system user or determined by the stimulation site selector circuit231. In some examples, the VVD can be set to zero such that LV pacingand RV pacing are simultaneously delivered. In another example, at leastsome table entries may include a recommended intra-LV time offset(ILVD). The ILVD represents an offset between LV pacing pulsesseparately delivered at different LV sites within a cardiac cycle when aLV MSP is selected by a system user or determined by the stimulationmode selector circuit 232. The LV MSP may be delivered via two or moreof the LV electrodes 161-164 as illustrated in FIG. 1.

The table 300 or 350 may be augmented to include information in additionto the stimulating timing parameters. In an example, at least someentries of the table 300 or 350 may additionally or alternativelyinclude information about stimulation site such as an indication ofLV-only pacing or a BiV pacing, or information about stimulation modesuch as an indication of SSP or MSP. As discussed above with referenceto FIG. 2, a selection between LV-only pacing or a BiV pacing, or aselection between SSP or MSP, may vary at different patient physical andphysiological conditions. The augmented table 300 or 350 thus providescomprehensive therapy recommendations on stimulation site, mode, andtiming values at various patient conditions. In an example, the entriesof the augmented table 300 or 350 may be constructed as a classstructure in the memory circuit 240 that contains values of one or moreof the stimulation site, mode, and timing parameters. For example, onetable entry may include (AVD, LV-only pacing), and another table entrymay include (AVD, BiV pacing, VVD, MSP, ILVD). In an example, oneelement in a table entry (e.g., AVD value, BiV pacing, or MSP) may beapplied to a number of table entries that share a common condition. Forexample, if BiV pacing is recommended for a condition defined by sittingposture, AS, and HR great than 100 bpm, then BiV pacing may berecommended for all conditions as long as containing a “sitting”posture, regardless of heart rate ranges, or atrial activation mode (ASor AP). In another example, if MSP is recommended for a conditiondefined by standing posture, AS, and HR within 70-80 bpm, then MSP maybe recommended for all conditions as long as containing a “standing”posture, regardless of heart rate ranges, or atrial activation mode.

In some examples, multiple tables of stimulation timing parameter valuesmay be constructed and stored in the memory circuit 240, such as an AVDtable containing only AVD values under various patient conditions, a VVDtable containing only VVD values under various patient conditions, or anILVD table containing only ILVD values under various patient conditions.The tables may include different patient physiological or functionalconditions. In an example, the stimulation timing adjuster circuit 233may refer to the VVD table to determine an optimal VVD value under aspecific patient condition when a BiV pacing is selected, such as viathe stimulation site selector circuit 231. In another example, thestimulation timing adjuster circuit 233 may refer to the ILVD table todetermine an optimal ILVD value under a specific patient condition whenMSP mode is selected, such as via the stimulation mode selector circuit232. The stimulation timing adjuster circuit 233 may refer to AVD tableirrespective of the selection of stimulation site and the selection ofstimulation mode.

FIGS. 4A-B illustrate methods for initializing and updating astimulation parameter table, such as the table 300 or 350. The tableinitialization and update methods may be implemented in and executed bythe controller circuit 250 as illustrated in FIG. 2. As illustrated inthe flow chart 410 in FIG. 4A, table initialization begins at 411, wherepatient physiological and physical conditions to be included in thetable are received. An impact of the patient condition on cardiacresponses and patient hemodynamics may be analyzed. In an example, theimpact of patient condition may be assessed using a change in P wave toR wave interval (PRI) (such as measured from a ECG or an intracardiacEGM), thoracic impedance, heart sounds, or pulse transit times under aspecified patient physiological or functional condition from theirrespective baseline measurements. Patient conditions having an impact onpatient hemodynamic responses or cardiac responses may be included inthe stimulation parameter table.

At 412, a testing protocol may be executed. The testing protocol mayinclude establishing various patient conditions, such as having thepatient to maintain a specific posture, inducing patient heart rate(e.g., through atrial pacing or through controlled exercise) to aspecified heart rate range, or establishing other patient conditions.The PRI during atrial sense AS, or the AVI during atrial pace AP, may bemeasured. The measurement of PRI or AVI may include sensing ventricularresponse at one or more of an RV sensing (RVS) site or an LV sensing(LVS) site, such as using an RV sensing vector comprising an RVelectrode (e.g., one of 152-154), or an LV sensing vector comprising anLV electrode (e.g., one of 161-164). The RV or LV sensing vector may bea unipolar sensing vector comprising an RV or LV sensing electrode as acathode and the device can 112 as an anode. In an example, the PRI orAVI measured at 412 may include one of more of AS to RVS interval, AS toLVS interval, AP to RVS interval, and AP to LVS interval. In someexamples, the testing protocol may include acquiring additionalinformation such as patient echocardiography-derived measurements, orother hemodynamic parameters or clinical diagnostics under variouspatient conditions.

At 413, one or more stimulation timing parameters, such as AVD, may becomputed using the PRI or AVI measurements or optionally along withother information acquired at 412. Sensed AVD and paced AVD may each becomputed using a combination of the PRI or AVI measured at the RV andLV. In an example, the AVD is determined using a weighted combination,such as in the following equation:

AVD=k1*AV_(R) +k2*AV_(L) +k3  (1)

In Equation (1), the AV_(R) denotes the interval between AS or AP toRVS, and the AV_(L) denotes the interval between AS or AP to LVS. In anexample, if the inter-ventricular interval between RV and LV,Δ_(LR)=AV_(L)−AV_(R), is less than zero, then AVD may be computed usingonly the AV_(L), that is, AVD=k2*AV_(L). In an example, k2 isapproximately between 0.5 and 1. If Δ_(LR) is equal to or greater thanzero, then AVD may be computed as a weighted combination of AV_(R) andAV_(L), as given in Equation (1) above. The weight factors k1 and k2,and the scalar bias k3, may be chosen according to synchrony of the LVand RV sensing. In an example, the weight factors may be empiricallydetermined using pacing data from patient population, data obtained fromechocardiography study, or other clinical diagnostics. In an example,weight factors may respectively generated and used to compute AVD fordifferent ventricular stimulation site (LV-only or BiV), or fordifferent LV lead location (e.g., anterior LV or free wall).

In some examples, the AVD computation may additionally include a beatscreening process. A sufficient number (e.g., 3-20) of LVS or RVS beatsthat satisfy a sensing criterion during AS is required to obtain a morereliable sensed AVD. Similarly, a sufficient number (e.g., 3-20) of LVSor RVS beats that satisfy a sensing criterion during AP is required toobtain a more reliable paced AVD. In an example, a median, a mean, orother central tendency over a plurality of PRI or AVI measurements isused to determine the AVD, such as according to Equation (1). In someexamples, if there is no sufficient LVS or RVS beats within a specifiedtime or a number of cardiac cycles, then the paced AVD can be determinedusing the sensed AVD. In an example, if Δ_(LR) is greater than zeromilliseconds (msec), then the sensed AVD may be determined to beapproximately 60 msec longer than the sensed AVD. If Δ_(LR) is equal toor less than zero msec, then the sensed AVD may be determined to beapproximately 45 msec longer than the sensed AVD.

The AVD thus determined depends on RVS or LVS. In some examples, the RVor LV sensing electrode may be different from the RV or LV pacingelectrode. Because the AVD is estimated using the measurement from theRV or LV sensing electrode, the estimated AVD may not be optimal whenapplied to a different RV or LV pacing electrode to deliver a pacingtherapy, at least because of a time offset (ASP) between cardiacactivations at the sensing electrode site and the pacing electrode site.Referring to FIG. 1, by way of example and not limitation, a sensingelectrode LV1 161 is used for measuring the AV_(L) (the interval betweenAS or AP to LVS), while the LV pacing is delivered via a LV pacingvector comprising a different electrode LV3 163 and the can 112. Thesensing-pacing electrode time offset Δ_(SP) between the electrodes LV1and LV3, may be measured under a known patient condition, and appliedover to other patient conditions. By way of example and not limitation,the Δ_(SP) may be measured under a relatively easily manageable patientcondition, such as pacing at a lower rate limit (LRL) when the patientis in a prone position. The measured Δ_(SP) may be stored in the memorycircuit 240 for future use.

At 414, if it is determined that the RV or LV sensing electrode isdifferent from the RV or LV pacing electrode, then at 415 the AVD atvarious patient conditions, including conditions different from theeasily manageable condition under which the Δ_(SP) is determined, may becorrected by adding the sensing-pacing electrode time offset Δ_(SP). Thecorrected AVD may be added to the stimulation parameter table at 416. Ifat 414 the same ventricular electrode is used for ventricular sensingand ventricular pacing, then no AVD correction is necessary; the AVDcomputed at 413 may be added to the stimulation parameter table at 416.In some examples, conditions under which the AVD are computed, such asthe HR range, patient posture, atrial activation mode (e.g., AS or AP),or time of a day as illustrated in FIGS. 3A-3B, may be screened againsttheir respective interactive limits. For example, under a particularpatient condition, the AVD may be determined when the pacing rate islimited by the lower rate limit (LRL) and/or the maximum tracking rate(MTR). The interactive limits may be programmed to the system or devicethat executes the testing protocol. Such interactive limits for thepatient conditions can be beneficial for safe operation during theexecution of the testing protocol in the table initialization as well asduring electrostimulation therapy according to the AVD values in thetable.

FIG. 4B is a flow chart 420 illustrating a method of updating thestimulation parameter table, such as a table created using the method410. The table may be updated periodically at specified time, such asevery minute, every few minutes, every hour, every day, every aspecified few days, every week, every month, etc. In some examples, thefrequency of table update may be determined using table update history,such as a trend of table update. The next table update may then bescheduled according to the historical trend. For example, the next tableupdate may be scheduled to be no longer than the shortest update period(i.e., time interval between two adjacent updates) within a timespan(e.g., a year) in patient history.

The update of the stimulation parameter table may be performed on theentire table or a portion of the table, such as those table entriescorresponding to one specific condition (e.g., standing posture). Thefrequency of table update may vary for different portions of the table,such that one portion of the table may be updated more frequently thananother portion of the table. In an example, table entries correspondingto more commonly occurred conditions, such as lower HR ranges (e.g.,<100 bpm), may be updated more frequently than table entriescorresponding to uncommon or less attainable conditions such as higherhear ranges (e.g., >100 bpm).

Additionally or alternatively, the table update may be triggered by aspecific event. At 421, trigger events for table update are monitored,including, for example, amount (e.g., percentage) of pacing therapypatient received over a specified time period, worsening heart failureor decompensation events, hemodynamic response trend to CRT, heart rate,posture, physical activity, heart sounds, occurrence of intrinsic beats,a sudden big change in AVD recommendation, among others. In an example,table update frequency may be determined based on variability of PRI orAVI under specified patient condition. In an example, a variance, astandard deviation, a range, or other measures of spreadness may becomputed from a plurality of PRI or AVI under specific patientconditions. A higher PRI variability, such as when exceeding a specifiedthreshold, may indicate an irregular AV conduction and less efficientcardiac function under specific patient conditions. This may triggerassessment and update of the stimulation parameter table.

If at 422 one or more trigger events occur and satisfy specificconditions (e.g., exceeding a threshold value or falling within aspecified value range), then at 423, patient physiological or functionalconditions may be assessed to determine whether they continue to impactpatient cardiac or hemodynamic responses. Depending on the impacts, anexisting condition may be removed from the table, or a new condition maybe integrated into the table. At 424, the PRI during AS or AVI during APmay be re-measured under the updated conditions, and the AVD, or alongwith other timing parameters, may be determined, such as using a similarapproach as previously discussed with reference to FIG. 4A.

The update of the table entries, such as the AVD or other stimulationtiming parameters, require sensing of RV or LV activities (RVS or LVS,respectively) and measuring PRI or AVI. Conventionally, this may requireat least temporary suspension of ventricular pacing therapy. This may bedisadvantageous because even withholding the pacing for a short periodof time may cause detrimental patient outcome. To ensure uninterruptedpacing during table update, a method of dynamic PRI or AVI determinationmay be used, such as that discussed below with reference to FIG. 5. PRIor AVI may be estimated and the stimulation parameter table may beupdate without requiring a suspension of pacing therapy, or otherwisecompromising the ongoing pacing therapy.

PRI/AVI Determination while Pacing

FIG. 5 illustrates a method 500 for dynamically determining PRI or AVIduring pacing. The method 500 may be implemented in and executed by thesystem 200. Dynamically determined PRI or AVI may be used for updatingthe stimulation parameter table, switching between LV-only pacing andBiV pacing, switching between SSP and MSP, or other processes requiringan estimate of PRI or AVI without suspension of ventricular pacingtherapy.

The method 500 includes a process 510 for estimating an offset(Δ_(I-PF)) under a controlled patient condition, such as a known heartrate range and a known posture. The offset Δ_(I-PF) may be determinedbetween an AVD corresponding to a pseudofusion beat and a PRI or AVI. Apseudofusion beat is an electrocardiographic representation of a cardiacdepolarization produced by superimposition of an ineffectual pacingstimulus on an intrinsic cardiac depolarization, such as a spontaneousQRS complex on the ECG, or an intrinsic ventricular beat on aventricular EGM. Pseudofusion occurs when intrinsic heart rate is veryclose to the pacing rate. The pacing stimulus, such as a RV pacing spikeor an LV pacing spike delivered according to an AVD, is ineffectualbecause it temporally occurs within the absolute refractory period ofthe spontaneous QRS.

At 511, an AVD may be gradually adjusted, and the ventricular pacing maybe delivered according to the adjusted AVD. In an example, the AVD maybe initialized to a small value shorter than the PRI, and graduallyincrease at a specified step size, such as approximately 5-10 msec. Inanother example, AVD may start from a large initial value greater thanPRI and gradually decreases at a specified step size. Ventricular pacingmay be delivered at each of the gradually adjusted AVD value. Evokedcardiac responses to ventricular pacing may be monitored from ECG,intracardiac EGM, or a physiological sensor signal. In an example, theevoked cardiac responses includes morphologies of a cardiac electricalsignal sensed by an RV or LV sensing electrode. In another example, theevoked cardiac response includes morphologies of a heart sound signal ora signal indicative of cardiac mechanical response to pacing. Thepseudofusion has a characteristic morphology with superimposed pacingspike on the intrinsic QRS complex or intrinsic ventricular morphology.If at 513 the morphologies indicate that pseudofusion has occurred, thenfrom the superimposed waveform morphology, an individualized offsetΔ_(I-PF) may be measured as an interval between AVD_(PF) and theintrinsic PRI, that is, Δ_(I-PF)=PRI−AVD_(PF), where AVD_(PF) representsthe AVD that induces the pseudofusion. If no pseudofusion occurs at 513,adjustment of AVD may continue at 511. In some examples, the offsetΔ_(I-PF) may be in a range between approximately 10-15 msec. The offsetΔ_(I-PF) may be stored in the memory circuit 240 for future use.

A process of dynamic PRI or AVI determination may begin at 520 where aPRI estimation during pacing therapy (such as a CRT or MSP) may beperiodically triggered. The events that triggers PRI estimation mayinclude stimulation parameter table update, stimulation site update(e.g., switching between LV-only pacing and BiV pacing), or stimulationmode update (e.g., switching between SSP and MSP), among others. At 530,the AVD of the present, ongoing pacing therapy may be graduallyincreased, such as at a specified step size of approximately 5-10 msec.Ventricular pacing morphologies may be monitored during pacing atgradually lengthened AVD. If at 540 a pseudofusion morphology isdetected, then AVD adjustment process may be terminated, and the presentAVD corresponding to the pseudofusion, AVD_(PF)′, may be recorded. Notethat the AVD_(PF)′ is measured under the present patient condition,which may be different from the patient condition where the AVD_(PF) andΔ_(I-PF) are determined at 513. At 550, an estimated PRI, ePRI, at thepresent patient condition may be estimated using the AVD_(PF)′ and thestored offset Δ_(I-PF):

ePRI=AVD_(PF)′+Δ_(I-PF)  (2)

The estimation of the PRI according to (2) assumes the Δ_(I-PF) is notsubstantially affected by changing patient condition. Because the AVDextension at 530 stops at pseudofusion (at which point the pacingtherapy is still delivered) and never goes beyond that point, pacingtherapy can be effectively maintained during the PRI determinationprocess. Additionally, using the pre-stored Δ_(I-PF) may also reducetime for PRI or AVI computation, save battery power, and conservecomputational resources.

The estimated PRI or AVI may be used to update stimulation timingparameters, such as AVD according to Equation (1), or be used toreassess and select stimulation site between LV-only pacing and BiVpacing under various patient physiological or functional conditions, asto be discussed with reference to FIG. 6. Inter-ventricular delaybetween an RV sensing site and one or more LV sensing sites can bederived from the estimated PRI or AVI. The inter-ventricular intervalmay be used to assess stimulation mode selection between SSP and MSPunder various patient conditions, as to be discussed in the followingwith reference to FIG. 7.

Dynamic Stimulation Site Switching Between LV-Only Pacing and BiV Pacing

FIG. 6 illustrates an example of a method 600 for determining betweenLV-only pacing and BiV pacing. The method 600 may be implemented in andexecuted by the stimulation site selector circuit 231, as illustrated inFIG. 2. In an example, the method 600 may be used to determinestimulation site (LV-only pacing or BiV pacing) on a beat-by-beat basis,or to adjust the stimulation site periodically at specified time.

The method 600 begins at 610 where the patient physiological orfunctional conditions are identified. Patient conditions, such as heartrate, patient posture, physical activity, atrial activation mode, amongothers, may have an impact on the hemodynamic outcome during LV-onlypacing or BiV pacing. At 620, PRI or AVI are measured. The PRI may bemeasured from surface ECG, and AVI may be measured from an atrial sense(AS) or atrial pace (AP) event to a right ventricular sense (RVS) event.In an example, the PRI or AVI may be estimated while maintaining thepacing therapy, such as using the method 500 based on pseudofusiondetection. At 630, a trigger event is detected. The trigger event mayinclude a change in patient physiological or functional condition, suchas a posture change, physical activity intensity change, or a chronicchange in patient HF status such as a decompensation event. In anexample, the trigger event includes an increase in heart rate when thepatient maintains the current physiological or physical condition. Forexample, if X out of Y beats exceed a heart rate threshold, then astimulation site assessment may be triggered. In an example, three outof five consecutive beats exceeding a rate cutoff of 100 beats perminute (bpm) may trigger the stimulation site assessment. Alternatively,at 630, the stimulation site assessment may be performed periodically ata specified time.

If the heart rate criterion is satisfied at 630, the measured PRI may becompared to a PRI threshold. PRI_(TH), at 640. In an example, thePRI_(TH) is approximately in a range between 250-270 msec. In someexamples, the threshold PRI_(TH) may be determined for various patientconditions empirically, such as using echocardiography data or otherheart failure diagnostics. The PRI_(TH) may be patient conditiondependent, such that the PRI_(TH) at one patient condition may bedifferent from the PRI_(TH) at another different patient condition. Inan example, the PRI m may be heart rate dependent. The PRI_(TH) at thedevice's lower rate limit (LRL) may be set to a first value, such asapproximately 270 msec. The PRI_(TH) at the device's maximum trackingrate (MTR) may be set to a lower value, such as approximately 200 msec.The PRI_(TH) at heart rates between the LRL and MTR may be interpolatedbetween 200 msec and 270 msec using a linear, piece-wise linear,exponential, or other nonlinear curve. If the PRI exceeds the patientcondition-indicated threshold PRI_(TH), then a BiV pacing is recommendedat 650.

If the PRI does not exceed the threshold PRI_(TH), variability of thePRI may be evaluated at 660. The variability may be measured using avariance, a standard deviation, a range, or other measures of spreadnessfrom a plurality of PRI or AVI under the specified patient condition. Ifat 660 the PRI variability exceeds a patient condition-indicated PRIvariability threshold PRIvar_(TH) then BiV pacing is recommended at 650.A more variable PRI may indicate irregular AV conduction and cardiacfunction deterioration, in which case a BiV pacing may be preferred overthe LV-only pacing to provide enhanced synchronous ventricularcontractions and improved cardiac performance. If PRI is notsubstantially lengthened (e.g., falling below the threshold PRI_(TH))and is less variable (e.g., falling below the variable thresholdPRIvar_(TH)), then LV-only pacing may be recommended at 670.

Stimulation site selection, or switching between LV-only and BiV pacing,may be performed on a beat-by-beat basis. Alternatively, to improvereliability of PRI and PRI variability measurements, the PRI and PRIvariability may be analyzed over a plurality of N heart beats, where Nis a positive integer. In an example, N is between 10 and 20 beats. TheN beats may be consecutive beats. Alternatively, the N beats may benon-consecutive. For example, a heart beat is sensed every 5-15 secondsand the PRI is computed from that heart beat, and N PRIs may be computedfrom the N beats. The decisions at 640 and 660 may be based on at leastM out of N heart beats show an extension of PRI (at 640) or increasedvariability (at 650). In an example, M is equal to or great than 50% oof N. In another example, the LV-only or BiV pacing decisions may beevaluated over a plurality of N beats. If LV-only pacing is recommendedfor all N beats, then LV is recommend at 670. If BiV pacing isrecommended for all N beats, or a mixture of LV-only pacing andBiV-pacing across the N beats, then BiV pacing is recommended at 650.

The method 600 determines between LV-only pacing and BiV pacing based onAV conduction property, including an extension or increased variabilityof PRI or AVI. The method 600 may additionally using sensedinter-ventricular interval to determine the stimulation site. Theinter-ventricular interval represents the activation delay between LVand RV, and may be computed as a difference between (1) the AS to RVSinterval and (2) the AS to LVS interval, or a difference between (1) theAP to RVS interval and (2) the AP to LVS interval. In an example, if theinter-ventricular interval is less than a threshold (e.g., 20 msec),which may indicate an absence of left bundle branch block, then BiVpacing is recommended at 650. If the inter-ventricular interval is equalto or greater than the threshold (indicating RV activation substantiallylags behind LV activation, such as exceeding 20 msec), then the PRI andPRI variability criteria at 640 and 660 may be applied to determinebetween the LV-only pacing and the BiV pacing.

In some examples, information about LV lead position may be included inthe method 600 to determine the stimulation site. The lead position maybe provided by a user or received through the patient condition receiver220. In an example, even if the PRI and PRI variability criteria at 640and 660 recommends a BiV pacing, if the LV lead is in an anteriorposition, then LV-only pacing is instead recommended.

Dynamic Stimulation Mode Switching Between SSP and MSP

FIG. 7 illustrates an example of a method 700 for determining betweenSSP pacing and MSP. The method 700 may be implemented in and executed bythe stimulation mode selector circuit 232 as illustrated in FIG. 2. Inan example, the method 700 may be used to determine stimulation mode(SSP or MSP) on a beat-by-beat basis, or to adjust the stimulation siteperiodically at specified time.

The method 700 begins at 710 where the patient physiological orfunctional conditions are identified. Patient conditions, such as heartrate, patient posture, physical activity, atrial activation mode, amongothers, may have an impact on the hemodynamic outcome during SSP or MSP.At 720, inter-ventricular interval may be respectively measured at aplurality of candidate LV sites {LV(i)}. The resulting inter-ventricularintervals {D(i)} represent respectively degrees of dyssynchrony betweenRV and various LV sites {LV(i)}. In an example, RVS may be sensed usingan RV sensing vector comprising one of the RV electrodes 152-154, andLVS may be sensed at two or more LV sites using sensing vectors thateach comprise one of the LV electrode 161-164. The inter-ventricularinterval may be computed as a difference between (1) the AS to RVSinterval and (2) the AS to LVS interval. Alternatively, theinter-ventricular interval may be computed as a difference between (1)the AP to RVS interval and (2) the AP to LVS interval. For example, fora particular LV site LV(j), the corresponding inter-ventricular intervalD (j)=AV_(R)−AV_(L)(j), where AV_(R) denotes the delay between AS or APto RVS, and the AV_(L)(j) denotes the delay between AS or AP to LVSsensed at j-th LV site LV(j). In an example, the AV_(R) or AV_(L) may bemeasured while maintaining the pacing therapy, such as using the method500 based on pseudofusion detection.

At 730, a trigger event is detected. The trigger event may include achange in patient physiological or functional condition, such as aposture change, physical activity intensity change, or a chronic changein patient HF status such as a decompensation event. In an example, thetrigger event includes an increase in heart rate. If X out of Y beatsexceed a heart rate threshold, then a stimulation site assessment may betriggered. In an example, three out of five consecutive beats exceedinga rate cutoff of 100 bpm may trigger the stimulation mode assessment.Alternatively, stimulation mode assessment may be performed periodicallyat specified time.

If the heart rate criterion is satisfied at 730, then at 740 thestimulation mode assessment is triggered, and the inter-ventricularintervals {D(i)} corresponding to the LV sites (LV(i)) may each becompared to an inter-ventricular delay threshold D_(TH). In an example,the threshold D_(TH) may be determined for various patient conditions,such as using echocardiography data or other heart failure diagnostics.The threshold D_(TH) may be patient condition dependent, such that thethreshold D_(TH) at one patient condition may be different from thePRI_(TH) at another different patient condition. An LV site, such asLV(i), may be selected for delivering pacing if the correspondinginter-ventricular interval, D(i), exceeds the threshold D_(TH). Forexample, because the threshold D_(TH) is patient-indication dependent,an LV site LV(i) may be selected for prone posture, while a different LVsite LV(j) may be selected for standing posture. If at 740, two or moreLV sites satisfy the inter-ventricular interval criterion, then the LVelectrodes at those LV sites are selected for delivering MSP at 760. Ifonly one LV site satisfies the inter-ventricular interval criterion,then SSP using the LV electrode at that site is recommended at 750. Ifnone of the LV sites satisfies the inter-ventricular interval criterion,then SSP is recommended at 750 using the LV electrode that correspondsto the longest inter-ventricular interval among the candidate LV sites{LV(i)}.

Non-Transient Machine Readable Medium

FIG. 8 illustrates a block diagram of an example machine 800 upon whichany one or more of the techniques (e.g., methodologies) discussed hereinmay perform. Portions of this description may apply to the computingframework of various portions of the LCP device, the IMD, or theexternal programmer.

In alternative embodiments, the machine 800 may operate as a standalonedevice or may be connected (e.g., networked) to other machines. In anetworked deployment, the machine 800 may operate in the capacity of aserver machine, a client machine, or both in server-client networkenvironments. In an example, the machine 800 may act as a peer machinein peer-to-peer (P2P) (or other distributed) network environment. Themachine 800 may be a personal computer (PC), a tablet PC, a set-top box(STB), a personal digital assistant (PDA), a mobile telephone, a webappliance, a network router, switch or bridge, or any machine capable ofexecuting instructions (sequential or otherwise) that specify actions tobe taken by that machine. Further, while only a single machine isillustrated, the term “machine” shall also be taken to include anycollection of machines that individually or jointly execute a set (ormultiple sets) of instructions to perform any one or more of themethodologies discussed herein, such as cloud computing, software as aservice (SaaS), other computer cluster configurations.

Examples, as described herein, may include, or may operate by, logic ora number of components, or mechanisms. Circuit sets are a collection ofcircuits implemented in tangible entities that include hardware (e.g.,simple circuits, gates, logic, etc.). Circuit set membership may beflexible over time and underlying hardware variability. Circuit setsinclude members that may, alone or in combination, perform specifiedoperations when operating. In an example, hardware of the circuit setmay be immutably designed to carry out a specific operation (e.g.,hardwired). In an example, the hardware of the circuit set may includevariably connected physical components (e.g., execution units,transistors, simple circuits, etc.) including a computer readable mediumphysically modified (e.g., magnetically, electrically, moveableplacement of invariant massed particles, etc.) to encode instructions ofthe specific operation. In connecting the physical components, theunderlying electrical properties of a hardware constituent are changed,for example, from an insulator to a conductor or vice versa. Theinstructions enable embedded hardware (e.g., the execution units or aloading mechanism) to create members of the circuit set in hardware viathe variable connections to carry out portions of the specific operationwhen in operation. Accordingly, the computer readable medium iscommunicatively coupled to the other components of the circuit setmember when the device is operating. In an example, any of the physicalcomponents may be used in more than one member of more than one circuitset. For example, under operation, execution units may be used in afirst circuit of a first circuit set at one point in time and reused bya second circuit in the first circuit set, or by a third circuit in asecond circuit set at a different time.

Machine (e.g., computer system) 800 may include a hardware processor 802(e.g., a central processing unit (CPU), a graphics processing unit(GPU), a hardware processor core, or any combination thereof), a mainmemory 804 and a static memory 806, some or all of which may communicatewith each other via an interlink (e.g., bus) 808. The machine 800 mayfurther include a display unit 810 (e.g., a raster display, vectordisplay, holographic display, etc.), an alphanumeric input device 812(e.g., a keyboard), and a user interface (UI) navigation device 814(e.g., a mouse). In an example, the display unit 810, input device 812and UI navigation device 814 may be a touch screen display. The machine800 may additionally include a storage device (e.g., drive unit) 816, asignal generation device 818 (e.g., a speaker), a network interfacedevice 820, and one or more sensors 821, such as a global positioningsystem (GPS) sensor, compass, accelerometer, or other sensor. Themachine 800 may include an output controller 828, such as a serial(e.g., universal serial bus (USB), parallel, or other wired or wireless(e.g., infrared (IR), near field communication (NFC), etc.) connectionto communicate or control one or more peripheral devices (e.g., aprinter, card reader, etc.).

The storage device 816 may include a machine readable medium 822 onwhich is stored one or more sets of data structures or instructions 824(e.g., software) embodying or utilized by any one or more of thetechniques or functions described herein. The instructions 824 may alsoreside, completely or at least partially, within the main memory 804,within static memory 806, or within the hardware processor 802 duringexecution thereof by the machine 800. In an example, one or anycombination of the hardware processor 802, the main memory 804, thestatic memory 806, or the storage device 816 may constitute machinereadable media.

While the machine readable medium 822 is illustrated as a single medium,the term “machine readable medium” may include a single medium ormultiple media (e.g., a centralized or distributed database, and/orassociated caches and servers) configured to store the one or moreinstructions 824.

The term “machine readable medium” may include any medium that iscapable of storing, encoding, or carrying instructions for execution bythe machine 800 and that cause the machine 800 to perform any one ormore of the techniques of the present disclosure, or that is capable ofstoring, encoding or carrying data structures used by or associated withsuch instructions. Non-limiting machine readable medium examples mayinclude solid-state memories, and optical and magnetic media. In anexample, a massed machine readable medium comprises a machine readablemedium with a plurality of particles having invariant (e.g., rest) mass.Accordingly, massed machine-readable media are not transitorypropagating signals. Specific examples of massed machine readable mediamay include non-volatile memory, such as semiconductor memory devices(e.g., Electrically Programmable Read-Only Memory (EPROM), ElectricallyErasable Programmable Read-Only Memory (EEPROM)) and flash memorydevices; magnetic disks, such as internal hard disks and removabledisks; magneto-optical disks; and CD-ROM and DVD-ROM disks.

The instructions 824 may further be transmitted or received over acommunications network 826 using a transmission medium via the networkinterface device 820 utilizing any one of a number of transfer protocols(e.g., frame relay, internet protocol (IP), transmission controlprotocol (TCP), user datagram protocol (UDP), hypertext transferprotocol (HTTP), etc.). Example communication networks may include alocal area network (LAN), a wide area network (WAN), a packet datanetwork (e.g., the Internet), mobile telephone networks (e.g., cellularnetworks), Plain Old Telephone (POTS) networks, and wireless datanetworks (e.g., Institute of Electrical and Electronics Engineers (IEEE)802.11 family of standards known as WiFi®, IEEE 802.16 family ofstandards known as WiMax®), IEEE 802.15.4 family of standards,peer-to-peer (P2P) networks, among others. In an example, the networkinterface device 820 may include one or more physical jacks (e.g.,Ethernet, coaxial, or phone jacks) or one or more antennas to connect tothe communications network 826. In an example, the network interfacedevice 820 may include a plurality of antennas to wirelessly communicateusing at least one of single-input multiple-output (SIMO),multiple-input multiple-output (MIMO), or multiple-input single-output(MISO) techniques. The term “transmission medium” shall be taken toinclude any intangible medium that is capable of storing, encoding orcarrying instructions for execution by the machine 800, and includesdigital or analog communications signals or other intangible medium tofacilitate communication of such software.

Various embodiments are illustrated in the figures above. One or morefeatures from one or more of these embodiments may be combined to formother embodiments.

The method examples described herein can be machine orcomputer-implemented at least in part. Some examples may include acomputer-readable medium or machine-readable medium encoded withinstructions operable to configure an electronic device or system toperform methods as described in the above examples. An implementation ofsuch methods may include code, such as microcode, assembly languagecode, a higher-level language code, or the like. Such code may includecomputer readable instructions for performing various methods. The codecan form portions of computer program products. Further, the code can betangibly stored on one or more volatile or non-volatilecomputer-readable media during execution or at other times.

The above detailed description is intended to be illustrative, and notrestrictive. The scope of the disclosure should therefore be determinedwith references to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. A system, comprising: a stimulation control circuit configured to:determine atrioventricular (AV) conduction characteristics for aplurality of heart rates or heart rate ranges; store, in a memory, afirst pacing site configuration associated with a first subset of the AVconduction characteristics for the plurality of heart rate or heart rateranges, and a second pacing site configuration associated with a secondsubset of the AV conduction characteristics for the plurality of heartrate or heart rate ranges; and select the first pacing siteconfiguration or the second pacing site configuration for deliveringcardiac stimulation according to an AV conduction characteristic at asensed heart rate.
 2. The system of claim 1, wherein: the AV conductioncharacteristics include atrioventricular intervals or atrioventricularinterval variability; the first pacing site configuration includesleft-ventricular (LV) only pacing and the second pacing siteconfiguration includes a bi-ventricular (BiV) pacing of both left andright ventricles; and the cardiac stimulation control circuit isconfigured to select the LV-only pacing or the BiV pacing according toan atrioventricular interval or an atrioventricular interval variabilityat a sensed heart rate.
 3. The system of claim 2, wherein the cardiacstimulation control circuit is configured to select the BiV pacing whenthe atrioventricular interval exceeds a first threshold.
 4. The systemof claim 2, wherein the cardiac stimulation control circuit isconfigured to select the BiV pacing when the atrioventricular intervalvariability exceeds a second threshold.
 5. The system of claim 2,wherein the cardiac stimulation control circuit is configured to selectthe LV-only pacing when the atrioventricular interval falls below afirst threshold and the atrioventricular interval variability fallsbelow a second threshold.
 6. The system of claim 1, wherein the AVconduction characteristics are determined for atrial sensed (AS) eventsand atrial paced (AP) events, and the stimulation control circuit isconfigured to select the first pacing site configuration or the secondpacing site configuration according to an AV conduction characteristicfor an AS or AP event at a sensed heart rate.
 7. The system of claim 1,wherein the stimulation control circuit is configured to store in thememory a stimulation parameter table that includes the first and secondpacing site configurations for the AS and AP events and corresponding tothe plurality of heart rates or heart rate ranges.
 8. A system,comprising: a stimulation control circuit configured to: determineinterventricular (VV) conduction characteristics between patient leftand right ventricles for a plurality of heart rates or heart rateranges; store, in a memory, a first pacing site configuration associatedwith a first subset of the VV conduction characteristics for a pluralityof heart rate or heart rate ranges, and a second pacing siteconfiguration associated with a second subset of the VV conductioncharacteristics for a plurality of heart rate or heart rate ranges; andselect the first pacing site configuration or the second pacing siteconfiguration for delivering cardiac stimulation according to a VVconduction condition characteristic at a sensed heart rate.
 9. Thesystem of claim 8, wherein: the VV conduction characteristics includeinter-ventricular intervals; the first pacing site configurationincludes a single-site left ventricular pacing (SSP) and second pacingsite configuration includes a multi-site left ventricular pacing (MSP)at two more left-ventricular sites; and the cardiac stimulation controlcircuit is configured to select the SSP or the MSP according to aninter-ventricular interval at a sensed heart rate.
 10. The system ofclaim 9, wherein the cardiac stimulation control circuit is configuredto measure inter-ventricular intervals between a right ventricular siteand a plurality of left ventricular sites, and to select the SSP or theMSP based on a number of the plurality of left ventricular sites havingthe corresponding inter-ventricular intervals satisfying a condition.11. The system of claim 10, wherein the cardiac stimulation controlcircuit is configured to select the MSP when at least twoleft-ventricular sites have respective inter-ventricular intervalsexceeding an inter-ventricular interval threshold.
 12. The system ofclaim 10, wherein the cardiac stimulation control circuit is configuredto select the SSP when no more than one left-ventricular site has aninter-ventricular interval exceeding an inter-ventricular intervalthreshold.
 13. A method of operating a system to control cardiacstimulation, the method comprising: determining, via a stimulationcontrol circuit, atrioventricular (AV) conduction characteristics for aplurality of heart rates or heart rate ranges, storing, in a memory, afirst pacing site configuration associated with a first subset of the AVconduction characteristics for the plurality of heart rate or heart rateranges, and a second pacing site configuration associated with a secondsubset of the AV conduction characteristics for the plurality of heartrate or heart rate ranges; and selecting the first pacing siteconfiguration or the second pacing site configuration for deliveringcardiac stimulation according to an AV conduction characteristic at asensed heart rate.
 14. The method of claim 13, wherein the first pacingsite configuration includes left-ventricular (LV) only pacing and thesecond pacing site configuration includes a bi-ventricular (BiV) pacingof both left and right ventricles, and selecting the first or secondpacing site includes selecting the LV-only pacing or the BiV pacingaccording to an atrioventricular interval or an atrioventricularinterval variability at a sensed heart rate.
 15. The method of claim 14,wherein selecting the first or second pacing site includes: selectingthe BiV pacing when the atrioventricular interval exceeds a firstthreshold, or when the atrioventricular interval variability exceeds asecond threshold; and selecting the LV-only pacing when theatrioventricular interval falls below the first threshold, and when theatrioventricular interval variability falls below the second threshold.16. The method of claim 13, wherein determining the AV conductioncharacteristics includes AV conduction characteristics for atrial sensed(AS) events and atrial paced (AP) events, and the selecting of the firstor second pacing site configuration is in accordance with an AVconduction characteristic for an AS or AP event at a sensed heart rate.17. The method of claim 13, comprising storing in the memory astimulation parameter table that includes the first and second pacingsite configurations for the AS and AP events and corresponding to theplurality of heart rates or heart rate ranges.
 18. The method of claim13, further comprising: determining interventricular (VV) conductioncharacteristics between patient left and right ventricles for aplurality of heart rates or heart rate ranges; and selecting between asingle-site left ventricular pacing (SSP) and a multi-site leftventricular pacing (MSP) at two more left-ventricular sites according toa VV conduction condition characteristic at a sensed heart rate.
 19. Themethod of claim 18, wherein the VV conduction characteristics includeinter-ventricular intervals between a right ventricular site and aplurality of left ventricular sites, and selecting the SSP or the MSPbased on a number of the plurality of left ventricular sites having thecorresponding inter-ventricular intervals satisfying a condition. 20.The method of claim 19, wherein selecting between SSP and MSP includes:selecting the MSP when at least two left-ventricular sites haverespective inter-ventricular intervals exceeding an inter-ventricularinterval threshold; and selecting the SSP when no more than oneleft-ventricular site has an inter-ventricular interval exceeding aninter-ventricular interval threshold.